This invention relates to a control device for a press secondary machining line which includes in combination at least two presses, a workpiece supplying unit, workpiece supplying and removing units, and a workpiece removing unit, these units being used to transfer or convey a workpiece which is formed by punching.
One example of a conventional press machining line is as shown in FIG. 1. A workpiece 2 conveyed by a belt conveyor 1 is loaded on a die 6 of a press 5 by the workpiece supplying hand 4 of a workpiece supplying unit 3. After being machined by the press 5, the workpiece 2 is removed to a stocker 9 by the workpiece removing hand 8 of a workpiece supplying and removing unit 7. The workpiece 2 on the stocker 9 is placed on a die 12 of another press 11 by the workpiece supplying hand 10 of the unit 7. After being pressed, the workpiece 2 is set on another stocker 15 by the workpiece removing hand of another workpiece supplying and removing unit 13. The workpiece 2 on the stocker 15 is placed on a die 18 of another press 17 by the workpiece supplying hand 16 of the unit 13. After being pressed, the workpiece 2 is removed by the workpiece removing hand 20 of a workpiece removing unit 19 and is then conveyed by a belt conveyor 21.
A variety of control devices are available for such a press secondary machining line as described above; however, a control device of the type that all presses in a line are operated simultaneously, is desirable because the control is simple and the number of times of machining per minute is relatively large. In order to operate the presses simultaneously, centralized control should be employed for the entire line. In the centralized control, all the control devices may be installed on one control board. However, in this case, the number of presses in a line is unavoidably limited, because the control devices should have different functions depending on the number of presses, and the number of workpiece supplying and removing units and the kinds of the same. Accordingly, it is rather difficult to increase or decrease the number of presses in a line. Furthermore, the centralized control system involves a problem to be solved that at the start of the operation, the presses should be operated one after another, and at the end of the operation the presses should be stopped successively; and a problem that, when a defective workpiece is removed from a press during the operation, the following presses must be stopped successively.